RFR: 8245938 Remove unused print_stack(void) method from XToolkit.c

[Alexander Scherbatiy]

Hello,

Could you review a simple cleanup 8245938 Remove unused 
print_stack(void) method from XToolkit.c

  Bug: https://bugs.openjdk.java.net/browse/JDK-8245938
  Fix: http://cr.openjdk.java.net/~alexsch/8245938/webrev.00

The unused print_stack function is removed from XToolkit.c.
The reason for the request is that execinfo is specific to glibc and is 
not supported by musl libc.

Thanks,
Alexander.